1. Technical Field
The present invention relates to telemetry devices. In particular, it relates to the control of I/O, power, and communications in RF telemetry devices which have integral power conservation and communications functions, are capable of attachment to user designed data collection and/or control devices and can be monitored by one or more servers or networks simultaneously with minimal power consumption and data transfer rates.
2. Background Art
The use of telemetry devices has proven useful for a variety of monitoring and measurement systems. Telemetry systems have been designed for monitoring data which is collected from locations that cover a wide geographic area. An example of one variety of telemetry based system which uses remote data acquisition devices and a central data collection system is a consumer billing system used to take periodic measurements of utility meters, such as those used for gas, electric and water. The use of these systems eliminates the need to have a utility company employee take measurements from the meter. As a result, the cost of data acquisition can be sharply reduced by eliminating or reducing the amount of manual labor required in a conventional utility billing system.
In a billing environment, such as that discussed above, the data acquisition device will remain dormant for substantial periods of time and be activated only for periodic measurements which are taken on a monthly basis or on a demand basis such as when service is terminated or initiated. An important feature for automated data acquisition systems such as this is the ability of the automated data acquisition system to operate unattended for extended periods of time. Some of these data acquisition devices use conventional wire based telephone lines while other variations use RF transmitters and receivers to communicate with a central data collection system. Often, data acquisition devices are battery powered. As a result, battery longevity and drainage issues are important concerns in many telemetry systems.
RF based systems provide an additional advantage in that the data acquisition device can work with data collection systems which are mobile. By installing the data collection system in a vehicle, the distance between the remote data acquisition device and data collection system is reduced. Due to the reduced distance, the power required by the remote data acquisition device to communicate with the central data collection system can be reduced. As a result, battery power conservation is improved and data collection costs are reduced. This can be very important in locations where power cannot easily be provided to the data acquisition device. However, the energy used to transmit the RF data is significant. In a system where the data acquisition device is frequently queried, the data transfers can have a negative impact on power management and battery life. It would be desirable to minimize the number of data transfers to conserve battery power and extend battery life.
Another technique used to reduce battery power consumption is to place the data acquisition device in a "sleep" mode, whereby the device normally rests in a low power state until activated by a signal demanding a data reading. When the signal is received, full power is applied to the data acquisition device, the data (e.g. meter reading) is read, the data is transmitted to the data collection system, and the data acquisition device is placed back in the sleep state until the next measurement is required. In the case of applications such as utility meter reading, high power levels need only be maintained for short time period once a month, resulting in greatly improved battery life. Of course, this type of power reduction is more useful for devices as the frequency of data acquisition decreases. This method of power conservation is useful for applications, such as utility billing systems, where activity is infrequent. However, many RF telemetry applications are used to transmit data on a frequent basis. For example, in agricultural environments, frequent measurements are required to determine when equipment such as irrigation devices should be activated. Likewise, telemetry devices used in security systems may require frequent or continuous operation. As a result, the effectiveness of the sleep mode technique is reduced for applications which require frequent data transmission.
In the case where many data acquisition devices are used, such as in a utility meter environment, there can be significant delays when waiting to individually power up each data acquisition device in a large group. Known techniques provide for simultaneous powering up of groups of data acquisition devices to reduce this time delay. Known techniques accomplish this by broadcasting a single wake-up signal to a selected group of data acquisition devices. As each data acquisition device transmits its data, it can then return to sleep mode asynchronously.
Another method of reducing power consumption has been to store measurement data in the data acquisition devices until they are periodically polled by the data collection system. This method reduces power requirements by reducing the amount of communication between the data acquisition device and the data collection system. While this approach can be useful in a single application system such as that used for water treatment systems, etc., it is not effective in environments where multiple independent applications access the same data acquisition device. Multiple application environments will cause multiple transmissions, resulting in excessive battery drain, even if data is stored in the data acquisition device for periodic data transmission. It would be desirable to have a way to minimize data traffic in multiple application environments such that power drain due to excessive transmission rates are avoided.
Performance in data acquisition systems is also a concern. Transmission of data between a data acquisition device and the data collection system can impact system performance. As the number of data acquisition stations and/or user applications increases, the overall data traffic increases. In a multiple application environment, applications on the same server system can contend with one another for a given data acquisition device. Likewise, applications using different servers can also contend for a given data acquisition device. As the number of data acquisition devices increases and the complexity of the systems which use those devices increases, data acquisition systems require ever increasing amounts of processing power, both at the central computer and at the remote data acquisition device, to accomplish their tasks. One known technique stores data in the data acquisition device such that it can be transmitted on demand to the data collection system. However, multiple application systems using this method still require multiple redundant data transmissions for each application. It would be desirable to reduce the level of communication between devices, such that system resource consumption could be reduced by eliminating redundant transmissions.
The foregoing examples concentrated on utility meter data collection as a method of illustrating general data acquisition and power conservation concerns. However, those skilled in the art will recognize that a variety of applications exist for the collection of data, including industrial, manufacturing, financial, security, and agricultural, to name just a few. Industrial processes may require monitoring of materials as they are processed. Manufacturing plants can be designed to control activity and parts delivery on an long assembly line. Remote devices such as ATMs can be monitored for maintenance and security. Security systems are needed for monitoring homes and businesses. Agricultural uses include control systems for fertilization and irrigation. As can be seen, data acquisition systems can be used for numerous purposes. However, the same problems discussed above in regard to utility billing systems can appear in all of these other applications.
While addressing the basic desirability of maximizing battery life, the prior art has failed to provide a method of minimizing high power activities such as data transmission. Further, the prior art has not provided a method of minimizing contention in high data rate systems which have multiple independent applications which share use of the data acquisition devices.